The invention concerns a blind-stitch sewing machine with an oscillating fabric deflector to bulge the sewing material fabric into the arcuate path of an arc needle. The minimum spacing between the fabric deflector and the path of the arc needle is adjustable by a control circuit including a sewing material sensor in relation to the thickness of the sewing material.
Blind-stitch sewing machines are known in the art as evidenced by German Pat. No. 25 11 568. In a typical design, the sewing material sensor is mounted near the stitch zone and is connected by link means to the fabric deflector, to adjust the minimum spacing of the fabric deflector relative to the thickness of the sewing material between a throat plate and the sewing material sensor, that is the distance up to which the fabric deflector driven by an oscillating shaft and oscillating synchronously with the arc needle may approach the needle's path.
In blind-stitch sewing machines for point wise sewing of material by means of a predetermined number of stitches while the fabric deflector is motionless, it is known to set the spacing of the fabric deflector from the arcuate path of the arc needle by means of a cam acting as a stop, wherein the cam may be rotated by an electric stepping motor. The stepping motor may be connected to an electric control circuit having a memory for several different spacings between the fabric deflector and the path of the arc needle when sewing takes place. These spacings can be requested individually by a selector connected to the control circuit and actuated manually, whereby the stepping motor correspondingly drives the cam (German Pat. No. 35 19 849).
Moreover, it is within the state of the art as regards to such blind-stitch sewing machines having oscillating fabric deflectors with manual setting of its least spacing from the path of the arc needle to provide an alarm emitting an acoustical and/or an optical warning signal in the event that too small a minimum fabric deflector spacing has been set. This alarm includes an electric switch which, in that case, is closed (British Pat. No. 9 98 628).
Similarly, spring loaded depressing means are known in such blind-stitch sewing machines which press the sewing material, during the sewing procedure, against the oscillating fabric deflector to prevent it from being shifted transversely to the direction of sewing upon entry of the arc needle (German Offenlegungsschrift 30 15 433).
Light barriers of various designs are known for use in sewing machines, including such barriers recognizing sewing material edges transverse to the direction of sewing (German Pat. No. 33 23 214 and German Offenlegungsschrift 35 19 729).
Lastly, it is known relative to blind-stitch sewing machines to make the oscillating drive shaft of the fabric deflector hollow and to rotatably rest it on an inner support shaft. The inner support shaft, in tunr, rests eccentrically in a housing or frame of the sewing machine so as to be driven in an oscillatory manner to assure interval operation of a sewing machine and to periodically change the spacing between the fabric deflector and the arcuate path of the arc needle (German Pat. No. 9 30 058).